Complete rearrangement of a multi-porphyrinic rotaxane by metallationndash;demetallation of the central coordination site

摘要

Complete rearrangement of a multi-porphyrinic rotaxane by metallationndash;demetallation of the central coordination site Myriam Linke, Jean-Claude Chambron, Val�erie Heitz, Jean-Pierre Sauvage* and Vincent Semetey Laboratoire de Chimie Organo-Min�erale, UMR 7513 du CNRS, Universit�e Louis Pasteur, Institut Le Bel, 4, rue Blaise Pascal, 67000 Strasbourg, France. E-mail: sauvage@chimie.u-strasbg.fr Received (in Basel, Switzerland) 22nd July 1998, Accepted 25th September 1998 A new multiporphyrinic 2rotaxane has been made in which a gold(III) porphyrin is part of the ring; rotation of the stringlike fragment within the ring between two diametrically opposed positions is triggered by metallationndash;demetallation of the central coordination site.In relation to molecular switches,1 machines and motors,2,3 it is of special interest to be able to control at will, amongst other properties, the shape of multicomponent molecular systems. The triggering signal, responsible for the rearrangement of the compound can be photochemical,4 electrochemical5 or chemical. 6 Catenanes and rotaxanes are ideally suited for undergoing large amplitude motions under the action of an external stimulus.7,8 In the present work, we show that complexing or decomplexing an appropriate metal in a coordination site can bring to close proximity, or spread a long distance apart, given porphyrinic components of the system. The principle is depicted in Fig. 1. The compound made and studied is a 2rotaxane in which the string-like fragment bears two zinc(ii) porphyrins as blocking groups.The ring through which the string is threaded incorporates a gold(iii) porphyrin. It should be noted that these metalloporphyrins are key components of multichromophoric systems undergoing photoinduced electron transfer and proposed as models of given fragments of the photosynthetic reaction centre.9 The organic compounds used as intermediates in the synthesis of the 2rotaxane are represented in Fig. 2. The tetraaryl porphyrin 1 was prepared in 6 yield using pyrrole and a 1 : 1 mixture of the appropriate aldehydes (CF3CO2H, in CH2Cl2 followed by chloranil treatment10). After metallation (KAuCl4) to afford 2 (76), demethylation (BBr3) furnished 3 in almost quantitative yield. 5 was obtained by reacting 411 with 2-bromoethanol (K2CO3, refluxing DMF) and it was converted to 6 (tosyl chloride, NEt3, CH2Cl2) and subsequently to 7 (NaI, acetone; 30 yield from 4).Macrocycle 11 was prepared from 3 and 7 (Cs2CO3 in DMF, 55 deg;C; 31 yield). Rotaxane 14 was synthesized following a strategy previously developed in our group for making porphyrin-stoppered rotaxanes.9 An equimolar mixture of 8, 11 and Cu(MeCN)4 + led quantitatively to prerotaxane 12 (not drawn) in which the open chain fragment 8 has been threaded through the ring 11 thanks to the gathering effect of copper(i). The terminal porphyrinic blocking groups of 13 were built from 9, 10 and 12 (CF3CO2H in CH2Cl2; chloranil). 14dagger; was obtained after metallation Zn(OAc)2 in 13 yield from 8.The conformation of 14 is indeed similar to what the drawing of Fig. 3 suggests. In particular, NOE effects measured on H5,6 and Hpy demonstrate unambiguously that a close proximity Fig. 1 Control of the mutual arrangement between the gold porphyrin (PAu+ incorporated in the ring, black diamond) and the zinc porphyrins (PZn endfunction of the dumbell, white diamond) by complexation/decomplexation of a metal centre (black circle) within/from the central coordination site. (a) The chemical structure of the two organic constitutive fragments of the rotaxane (ring and thread) is such that, in the complex, the gold porphyrin is remote from the two zinc porphyrins.(b) After removal of the central metal, weak forces may favour an attractive interaction between PAu+ and the PZn nuclei, leading to a situation in which PAu+ is pinched between the two PZn units. The interconversion between the situations (a) and (b) implies a half-turn rotation of the threaded fragment (axle) within the ring (wheel), the latter being artificially considered as fixed.This motion is reminiscent of the process taking place in the rotary motor of ATPsynthase. 3b Fig. 2 Intermediates used in the synthesis of the 2rotaxane. Chem. Commun., 1998, 2469ndash;2470 2469exists between the rear of the 1,10-phenanthroline nucleus belonging to the dumbbell-like fragment and the endocyclic part of the ring-embedded porphyrin. As indicated in Fig. 3, demetallation of 14 affords 15,dagger; this compound displaying a profoundly modified geometry as compared to 14. In particular, NOE effects show close proximity between Hm and HoA as well as between Hpy and HoA and between HoB and HMe, which indicates that the geometry of the molecule is roughly as depicted in Fig. 3. Space-filling models suggest that within the demetallated rotaxane 15, free rotation of the lsquo;axlersquo; within the ring can take place. The driving force for bringing PAu+ between the PZn units, playing the role of two jaws, is certainly related to the extremely different and complementary electronic properties of PAu+ (electron acceptor) and PZn (electron donor). Very approximate geometrical features can be estimated from the models.Of particular interest are the centre-to-centre (Aumiddot;middot;middot;Zn) and the edge-to-edge distances between PAu+ and PZn.The estimated centre-to-centre separation is ca. 19 and ca. 7 Aring; for 14 and 15 respectively. The edge-to-edge distance, which is more relevant to electron transfer, is ca. 12 and ca. 5 Aring; for 14 and 15, although it should be kept in mind that 15 is certainly very flexible, with difficult to estimate interatomic distances. Interestingly, the interconversion between 14 and 15, although leading to dramatic geometrical changes, is quantitative and reversible. This changeover process can be triggered by other metals such as Ag+ and Li+.We thank the Ministry of Education for a fellowship (to M. L.). Notes and references dagger; Selected data: 14: dH(CD2Cl2, 400 MHz) 10.13 (s, 4H), 9.60 (d, 2H), 9.47 (d, 2H), 9.43 (s, 2H), 9.30 (s, 2H), 8.90 (d, 2H), 8.52 (d, 2H), 8.42 (d, 4H), 8.31 (d, 2H), 8.17 (d, 4H), 8.13 (d, 4H), 8.04 (t, 2H), 7.98 (s, 2H), 7.97 (d, 2H), 7.89 (d, 4H), 7.86 (t, 2H), 7.78 (d, 4H), 7.75 (s, 2H), 7.62 (d, 4H), 7.54 (d, 4H), 6.63 (d, 4H), 4.95 (m, 4H), 4.41 (m, 4H), 3.95 (t, 8H), 3.81 (t, 8H), 2.44 (s, 12H), 2.17 (t, 8H), 2.06 (t, 8H), 1.84 (s, 12H), Aring; 1.68 (m, 16H), 1.60 (s, 36H), 1.51 (s, 36H), Aring; 1.50 (m, 16H), Aring; 1.40 (m, 16H), 0.87 (t, 12H), 0.83 (t, 12H); m/z (FAB) 3783.6 (M+); l(CH2Cl2)/nm 415, 538, 574. 15: dH(CD2Cl2, 400 MHz) 10.07 (s, 4H), 9.56 (d, 2H), 9.39 (d, 2H), 9.36 (s, 2H), 9.15 (d, 4H), 8.80 (s, 2H), 8.57 (d, 2H), 8.46 (d, 2H), 8.26 (d, 4H), 8.21 (d, 4H), 8.18 (d, 4H), 8.11 (d, 2H), 8.09 (d, 4H), 8.00 (t, 2H), 7.99 (d, 2H), 7.91 (d, 4H), 7.90 (s, 2H), 7.85 (d, 4H), 7.82 (t, 2H), 7.46 (s, 2H), 7.39 (d, 4H), 4.82 (m, 4H), 4.43 (m, 4H), 3.91 (t, 8H), 3.70 (t, 8H), 2.40 (s, 12H), 2.27 (s, 12H), 2.12 (t, 8H), 1.93 (t, 8H), 1.68 (t, 8H), 1.55 (s, 36H), 1.47 (s, 36H), Aring; 1.40 (m, 16H), Aring; 1.35 (m, 8H), Aring; 1.25 (m, 8H), Aring; 1.20 (m, 8H), 0.85 (t, 12H), 0.72 (t, 12H); m/z (FAB) 3720.6 (M+); l(CH2Cl2)/nm 413, 538, 574. 1 A. 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MacDonald, J. Am. Chem. Soc., 1960, 82, 4384; J. S. Lindsey, I. C. Schreiman, H. C. Hsu, P. C. Kearney and A. M. Marguerettaz, J. Org. Chem., 1987, 52, 827. 11 C. O. Dietrich-Buchecker, J.-P. Sauvage and J.-P. Kintzinger, Tetrahedron Lett., 1983, 24, 5095; C. O. Dietrich-Buchecker and J.-P. Sauvage, Tetrahedron, 1990, 46, 503. Communication 8/05746J Fig. 3 Metallationndash;demetallation of the rotaxane induces a complete changeover of the molecule. The most important proton connectivities, as determined by 2D 1H NMR, are indicated by double arrows. 2470 Chem Commun., 1998, 246